30G Bra Size
30G fits a 29–31 inch (74–79 cm) underbust and a full bust of about 38 inches (97 cm). Its sister sizes are 28H and 32DDD.
Last reviewed on 25 September 2026.
30G at a glance
| Underbust (band) | 29–31 in · 74–79 cm |
|---|---|
| Full bust | ≈ 38 in · 97 cm |
| Bust minus underbust | ≈ 8 in · 20 cm |
| Sister sizes (same cup volume) | 28H · 32DDD |
| UK / EU / FR / AU | 30F · 65G · 80G · 8F |
| One cup bigger | 30H |
| One cup smaller | 30DDD |
| Approx. top size | XS · UK 6–8 / US 2–4 |
Measurements for 30G
30G is built for an underbust ribcage measurement that falls in the 29–31 inch range, with a full-bust measurement around 38 inches. The band number — 30 — is a smaller band that needs to sit firmly without cutting in. The cup letter — G — describes the difference between the two measurements; a G cup (US) means the full bust is about eight inches larger than the underbust — the same volume is an F in UK sizing. At this volume, three-part cups and side support panels usually fit more cleanly than thin moulded cups.
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30G in Other Sizing Systems
EU, FR, and JP sizing read the band in centimetres, which is why 30G maps to 65G (EU), 80G (FR), and 65G (JP) — the same body, expressed in different units. AU sizing uses a small numeric scale (8F for this band). UK sizing shares the band number with the US but parts ways at the cup once you go past D, so 30G reads as 30F on a UK label.
Sister Sizes for 30G
These sizes have the same cup volume as 30G. Try them if the band feels too tight or too loose.
← Tighter band, bigger cup · Looser band, smaller cup →
Sister sizes are useful when the cup of your 30G fits well but the band is wrong — too loose by the end of the day, or too tight to clip up comfortably. Going one band smaller and one cup larger keeps the cup volume the same while tightening the band; going the other way loosens the band without losing cup space. Read the full sister-size matrix if you want to see how this works for every size at once.
Fit Tips for 30G
G cups generally need well-engineered bras with strong band tension and reinforced wires. Look for ranges that specialise in fuller-bust fitting rather than mainstream sizes that stop at DD.
If your 30G bra is gapping at the top of the cup, the cup may be too large or the wrong shape — try a demi-cup or balconette before assuming the size is wrong. If the centre piece between the cups (the gore) does not lay flat against your sternum, the cup is almost certainly too small; go up one cup. If the band rides up across your back during the day, the band has stretched out or was too loose to begin with — drop one band size and add one cup to keep the same cup volume.
For more detailed troubleshooting, the Fit Test on the home page covers six common visible problems and the size or shape change that usually addresses each one. The guide to measuring mistakes covers the most common reasons a calculation comes out wrong in the first place.
Related sizes
If 30G is close but not quite right, these neighbouring sizes are the most useful next places to look:
See every size at a glance on the full bra size index, or read how to measure your bra size if you are not sure 30G is right for you.
30G — frequently asked questions
What measurements are a 30G bra in inches and cm?
A 30G bra fits an underbust (ribcage) measurement of roughly 29 to 31 inches (74–79 cm) and a full-bust measurement of about 38 inches (97 cm). The cup letter G reflects the roughly 8-inch (20 cm) difference between those two numbers.
What size is equivalent to 30G? (sister sizes)
The sister sizes of 30G are 28H (tighter band, one cup letter up) and 32DDD (looser band, one cup letter down). They hold the same cup volume as 30G on a different band. Try a sister size when the cups of your 30G fit but the band feels too loose or too tight.
What is 30G in UK, EU, and other sizing systems?
30G (US) converts to 30F in UK sizing, 65G in EU sizing, 80G in French sizing, 8F in Australian sizing, and 65G in Japanese sizing. The body is the same; only the labelling system changes.
Is 30G a small or large bra size?
In terms of how common it is, this size pairs a small band with a fuller-bust cup. There is no universal "small" or "large" bra size — the same cup letter describes a different volume on every band — but within the full range BraCalc covers (bands 28–48, cups AA–H) this combination sits toward the compact end.
Is 30G a small, medium, large, or XL?
As a rough guide, a 30 band usually matches size XS in tops and bralettes — around UK dress size 6–8 (US 2–4). The band number drives this more than the cup letter, so 30G lands in the same letter size as other 30-band bras. With a fuller cup, many people go one size up in fitted tops so the bust has room. Letter sizing varies a lot between brands, so always check the brand's own chart.
What is the next size up or down from 30G?
Keeping the same 30 band, one size up in the cup is 30H, and one size down is 30DDD. If you want a bigger or smaller band but the same cup volume, use a sister size instead: 28H or 32DDD. Remember that the cup letter is relative to the band — 32G has more cup volume than 30G, not the same.
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